An encrypted e-mail service reportedly used by Edward Snowden is shutting down, presumably in response to an investigation of the NSA whistleblower's use of the service.

Ladar Levison, the owner of Lavabit, announced the move Thursday in a note posted to the service's home page. Although Levison's cryptic note doesn't mention Snowden by name, he does say that he's "been forced to make a difficult decision: to become complicit in crimes against the American people or walk away from nearly 10 years of hard work by shutting down Lavabit."

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In nonspecific language, Levison writes that he would like to discuss the reasons for the shut down but is prevented from doing so because "Congress has passed laws that say otherwise." Federal law prohibits subjects of national security investigations from discussing the details or even existence of the investigation.

Lavabit, which uses encryption to prevent messages from being read by anyone other the sender or recipient, was the service Snowden allegedly used to send a message to a Human Rights Watch representative in July.

Levison could not immediately be reached for further comment. An NSA representative deferred comment to the Justice Department, which has been contacted for comment. CNET will update this report when we learn more.

Levison's full statement:

My Fellow Users,

I have been forced to make a difficult decision: to become complicit in crimes against the American people or walk away from nearly ten years of hard work by shutting down Lavabit. After significant soul searching, I have decided to suspend operations. I wish that I could legally share with you the events that led to my decision. I cannot. I feel you deserve to know what's going on-the first amendment is supposed to guarantee me the freedom to speak out in situations like this. Unfortunately, Congress has passed laws that say otherwise. As things currently stand, I cannot share my experiences over the last six weeks, even though I have twice made the appropriate requests.

What's going to happen now? We've already started preparing the paperwork needed to continue to fight for the Constitution in the Fourth Circuit Court of Appeals. A favorable decision would allow me resurrect Lavabit as an American company.

This experience has taught me one very important lesson: without congressional action or a strong judicial precedent, I would _strongly_ recommend against anyone trusting their private data to a company with physical ties to the United States.

Sincerely,
Ladar Levison
Owner and Operator, Lavabit LLC

Snowden is wanted by the U.S. for leaking top-secret documents to the media about the NSA's surveillance practices. He had been hunkered down in a Moscow airport for several weeks but was finally able to leave last week after Russia offered Snowden temporary asylum for one year.